This invention relates to a novel method for obtaining a purified fraction from a mixture using a magnetic fluid. The invention finds particular use for obtaining a purified fraction of crop seed.
The seed crop as it comes from the field contains a variety of contaminants such as weed seeds, soil particles, and inert material. These contaminants must be removed after harvest to obtain pure, live, crop for replanting. Tolerance limits for these contaminants vary from state to state and are usually more restrictive for the export market. For example, in order to minimize the spread of soil-borne pathogens, the amount of soil in crop seed for export to Japan cannot exceed 0.03 percent by weight. Some other countries have even more restrictive limits.
Conventional methods of cleaning crop seed include separation procedures based on differences in the physical properties of the crop seed and the contaminants, such as size, weight, color, density or a combination thereof. Seed processors also use magnetic cleaning to separate seeds and contaminants having different surface textures, such as smooth crop seed from rough or sticky contaminants. In this process, the seed mixture is moistened, iron powder added and the mixture mixed. Contaminants which are rough in texture or sticky tend to pick up the powder whereas smooth seed does not. The mixture is then passed over a magnetic separator which separates the magnetized contaminants from the nonmagnetized seeds.
While the above techniques are useful where physical differences are sufficient for separation, when the crop seed and contaminants are the same size and texture, restrictive phytosanitary tolerances for export of crop seed cannot be met by the conventional methods.